What causes melasma? The cause of melasma is complex. The pigmentation is due to overproduction of melanin by the pigment cells, melanocytes, which is taken up by the keratinocytes (epidermal melanosis) and/or deposited in the dermis (dermal melanosis, melanophages).
There are five total papillary muscles in the heart; three in the right ventricle and two in the left. The anterior, posterior, and septal papillary muscles of the right ventricle each attach via chordae tendineae to the tricuspid valve. The anterior and posterior papillary muscles of the left ventricle attach via chordae tendineae to the mitral valve.
Overview of the heart valves and related structures. The atria are divided into the left atrium and the right atrium, which correspond to the left and right sides of the heart. They are situated just above the ventricles of the heart and are separated by the cuspid valves. The atria are built and held up by rigid endocardial muscle fibers that completely encompass the blood as it flows through them.